1. Field of Invention
The basic unit of archaeological exploration is the site, which has been defined as "any location which exhibits evidence of past human activity." The definition is purposefully vague so as to encompass every conceivable area which may prove useful to research, from a campsite which may contain only a few artifacts to a city of several hundred thousand people.
Sites are located by their unique characteristics, stone tools, or pottery fragments lying on the surface, vegetation differing from the immediately surrounding area which indicates that the site may have been cleared in prehistoric times, or suspicious looking mounds or depressions of regular form, which may have been man-made. Sites may also be located by exploration of areas which experience has indicated were most frequently occupied, river forks, the edge of a bluff overlooking a river valley, or a natural stone formation providing shelter.
Once the site is located, the archaeologist normally makes out a survey form, systematically recording the location of the site on a map and describing its features. Normally, the site is photographed and a sketch map drawn. The site is given a number for identification, which is used on all notes or materials obtained.
After all the sites in an area have been surveyed and the survey notes reviewed in detail, the archaeologist determines which sites to excavate, based on his own particular interests and the reason for his research.
A major purpose of excavation is to determine the specific location of individual objects recovered from the site. Horizontal location may indicate that certain areas of a site were set aside for tool making, cooking, or keeping or slaughtering animals. By knowing the exact horizontal location of objects received, the plan of a camp or village may be reconstructed and much insight as to the lifestyle of the inhabitants is provided. Vertical placement or stratigraphy, may indicate the presence of several different groups of people living on a given site at different times.
Horizontal placement is normally determined by use of a grid system of N-S, E-W lines dividing the surface of the site into a pattern of squares of equal area. The site is then sampled to determine the most desirable squares for excavating. A common method of sampling is digging test trenches at right angles to one another in an X, L or T shape. Squares determined to be most likely to be productive are then excavated one or one/half at a time.
Vertical placement is normally measured from the surface or from an arbitrary datum level. Each object located is carefully recorded, along with its horizontal and vertical placement.
2. Prior Art
Actual excavation is frequently done by means of a trowel or scoop. Earth is transferred to a bucket and then to a sifter for the recovery of artifacts.
Conventional archaeological sifting devices comprise a wooden frame forming shallow box structure having wire mesh attached as a floor. The frame is normally of such dimension and weight as to require that it be supported on legs and spaced at some distance from the dig site. This arrangment requires the archaeologist to transport buckets of earth from the dig site to the sifter, utilize the sifter, and return to the dig site for more earth.
The conventional sifter has disadvantages in that time and energy are expended in continually transporting earth to the sifter, waiting for others to finish using the sifter, and returning to the dig site.
In addition, as explained, an accurate determination of the placement of objects located is essential to the research of an archaeologist. Accurate placement is extremely difficult to determine when earth is sifted in large quantities as it tends to be when the sifter is some distance away. Disposal of waste material which accumulates beneath the conventional sifter is yet another disadvatage. The sifter must be positioned prior to commencement of excavation. During excavation, however, archaeologists may discover, from the artifacts found, that there is need for further exploration precisely in the area occupied by the sifter.
The article PARTIAL RECOVERY, AND SAMPLE BIAS: THE RESULTS OF SOME SIEVING EXPERIMENTS, by Sebastian Payne, taken from the book Papers In Economic Prehistory, E. S. Higgs, Cambridge University Press, describes several alternatives to the conventional sifter described above.
One of these is the throwscreen, a mesh, set nearly upright, against which the earth is thrown. Larger particles roll down the near side to the ground and are searched through. The throwscreen is commonly used but is generally considered inefficient and difficult to work with.
Common hand-held sieves are soemwhat better, but have the disadvantages of mesh size not being specifically adapted to archaeological work, having sides too high for objects to be easily located and picked out and being of insufficient volume for fast and efficient work. Finally, there are sieves designed especially for archaeological work. These must be custom built and are costly in terms of both time and money.
One such design comprises a stack of shallow-box like sieves resting on a roughly cubicle frame which is stationary and rests on the ground. It is not dissimilar to the conventional sifter described above except for its more permanent construction and the fact that it consists of a stack of sieves rather than a single sieve.